You may have heard on Gardeners’ Question Time about soil testing, to find out whether it’s acid, alkaline or neutral. It’s a basic of gardening because it will tell you what plants will grow well and what plants will need a bit of help to survive.
We measure the ‘pH’, as it’s known, with a soil tester. The tester will give a pH number that describes how acid or alkaline your soil is. A pH of 7.0 is considered neutral. An acid soil has a pH value below 7.0 and above 7.0 the soil is alkaline.
All is not lost is your soil isn’t quite right for the plants of your dreams. Lime can be added to increase soil pH (make it more alkaline) and acidifying materials are added to decrease soil pH.
You can test your soil pH using a kit available at garden centres. But for the best results, send a soil sample to a laboratory for detailed analysis. The Royal Horticultural Society (RHS) offers such a service here.
Interpreting the results of a soil pH test
A pH test measures soil acidity or alkalinity. A pH 7.0 is considered neutral. An acid soil has a pH value below 7.0. Above pH 7.0 the soil is alkaline.
pH 3.0 – 5.0: Very acid soil
Action: Add lime to raise the pH to above 5.0. The addition of lime can help break up acid clay soils
pH 5.1 – 6.0: Acid soil
Action: Add lime if other plants are grown
pH 6.1 – 7.0: Moderately acid soil
A pH 6.5 is the best general purpose pH for gardens, allowing a wide range of plants to grow.
Action: It is not usually necessary to add anything to improve soil pH at this level
pH 7.1 – 8.0: Alkaline soil
Action: Sulphur, iron sulphate and other acidifying agents can sometimes be added to reduce pH. Clay soils often require very large amounts of acidifying material and soils with bits of chalk or lime (think South Downs, Salisbury Plain) are not usually treatable.
There’s much more on soil on the Royal Horticultural Society website.
